In the drilling of oil wells, a drill bit and drill string is used to drill a well hole. After the well hole is drilled, a liner (or casing) may be run across the productive interval by using the drill pipe. With the liner in place, a cement slurry is pumped down through the drill pipe, through the liner, and into an annulus between the liner and a casing in the well hole to cement the liner in place and to keep production fluids in the liner.
Quite often well holes are not completely vertical. They can have substantial horizontal components. Wells with substantial horizontal components are called high angle extended reach wells. Running the liner through high angle extended reach well holes can be difficult because of friction between the liner and the well hole wall caused by the weight of the liner against the wall. Translational friction can be substantially reduced by rotating the liner while it is being run into the well hole.
The tools that have run liners into extended reach well holes have not generally rotated the liners while they were being run in due to the high torque required for rotation, although the tools permit liner rotations after run-in. Rotation is typically used to release the tools from the liners once the liners are in place. Consequently, it has not been possible to rotate the liners to reduce frictional drag when release-by-rotation tools are used.
U.S. patent application Ser. No. 418,510, filed Oct. 10, 1989, discloses a hydraulic release oil tool which avoids these problems with existing release tools. This application is assigned to the assignee of the present invention and is incorporated herein fully by this reference. The tool described in that application allows the liner to be rotated in either direction as it is run into the well hole, and it releases the liner upon application of hydraulic pressure in the drill string. It is preferred to provide a safety joint as a backup for the primary release joint. In the event that the primary release joint fails to operate, the safety joint can be used to separate the liner. The present invention is particularly suited for use as a backup safety joint in connection with the hydraulic release oil tool of U.S. patent application Ser. No. 418,510, filed Oct. 10, 1989, when rotation is desired. It can also be used independently or as a primary release tool in its own right.